Theresa May and European Council president Donald Tusk have held crunch brexit talks.
The Downing Street meeting comes a day before the Prime Minister is due to make a landmark speech on Britian's future relationship with the Union.
The two discussed the transition period while Mrs May reiteraterd her rejection of the draft withdrawal treaty published by the EU.
Europe's chief Brexit negotiator Michel Barnier said the UK's decision to quit the bloc shows it no longer wants to respect the rules.
Barnier said: "The bottom line is that we have to preserve this unique market that the British have chosen to leave unfortunately because they no longer want to respect the rules, but we must continue to rely on this unique market, because this is very important for our unity, our cohesion, and our economic progress too."
One of main sticking points remains Northen Ireland. The EU has proposed to incorporate the province in a customs union to avoid a hard border with the Republic.
May has said that no British PM could ever agree to this.